Membranes are used, for instance, in separation processes as selective barriers that allow certain chemical species to pass, i.e., the permeate, while retaining other chemical species, i.e., the retentate. Membranes are used in many applications, for example as biosensors, heparinized surfaces, facilitated transport membranes utilizing crown ethers and other carriers, targeted drug delivery systems including membrane-bound antigens, catalyst-containing membranes, treated surfaces, sharpened resolution chromatographic packing materials, narrow band optical absorbers, and in various water treatments which involve removal of a solute or contaminant, for example, dialysis, electrodialysis, microfiltration, ultrafiltration, reverse osmosis, nanofiltration and in electrolysis and in fuel cells and batteries.
There are a large number of supports or substrates for membranes. Specific physical and chemical characteristics to be considered when selecting a substrate include: porosity, surface area, permeability, solvent resistance, chemical stability, hydrophilicity, flexibility and mechanical integrity. Other characteristics may be important in certain applications.
In Mika et al., J. Membr. Sci., 108 (1995) pp 37 to 56, there is described a procedure for modifying microporous polypropylene and polyethylene membranes wherein 4-vinylpyridine is in situ polymerized into the pores of the membrane.